GIS--a proven tool for public health analysis.

This article proposes some practical guidelines for effectively utilizing geographic information systems (GIS) in the assessment of public health problems. GIS has been a tool of choice in Florida's Palm Beach County Health Department for over 10 years. It has been used with continuing success to clearly communicate public health problems and solutions.

The unique advantage that GIS offers is that users can superimpose a number of layers of geographical information, then selectively turn them on and off while trying to discover a meaningful pattern between potential causes and observed effects. A public health practitioner can gain useful insights into solving public health problems by examining the pattern of spatial relationships that a well-prepared map can often provide.

GIS can provide a better understanding of the information already available about a geographic location or individual points. It may help give new insights into existing relationships pertinent to that location, including new understandings of causal factors and the benefits to be obtained from measuring them, controlling them, or both. It also may suggest information that is needed but not yet available.

A map that showed "everything" would be messy, difficult to read, or just plain incomprehensible. A useful map is a series of compromises between readability and comprehensive totality, between simplicity and complexity, between almost absolute accuracy and rough approximation. There is no standard answer. A decision must be made about the purpose of the map, what it should show, how the data should be communicated, and how much preparation time is available. This process also requires (in GIS language) making decisions about the following parameters:

1. the number and scope of layers that can be turned on and turned off in the map.

2. the area covered and the scale of the map or maps, and

3. the projection of the map and its coordinate system.

Some pertinent questions should be answered before you proceed with your map:

1. What is the scope? Is it, for example, all arboviral cases for this year, or is the focus on West Nile virus only? Is it for your entire county, or for a much smaller area?

2. What is the purpose? Is it to identify public health issues that require priority attention? Is it to analyze underlying and interrelated causal factors? Is it to help in the deployment of scarce resources for mitigation?

3. Who is the audience? Do you want to communicate with professionals who have epidemiological insight, support services that need understanding, or perhaps the press, so as to communicate key information to the public?

4. How much detail is needed? Should the finished product be, for instance, a comprehensive, polished map to be used as a basis for allocating resources, or a preliminary map that enables you to take a fast look at a rapidly unfolding situation?

5. When is the map needed? Can you wait three days, or must you have it in half an hour?

6. How many map copies do you need, of what size? Do you need 12 letter-size copies, or do you want two larger maps?

These decisions are fairly easy to make once the purpose of the map has been agreed upon. They should remain relatively unchanged during the mapping project.

Once these basic items have been addressed, it is necessary to identify how layer information will be displayed. Some maps have only three or four information layers; others may have 20 or more. You will need to classify your information into each of the three GIS categories of layer information (point, line, or polygon). These layers can be selectively superimposed on each other to identify spatial relationships that could be key in helping solve your problem.

Point data allow the map to show individual events (such as malaria cases) or specific locations (such as locations of hazardous waste generators). For data of this type, you need to provide (or have available) standardized address information or, ideally, GPS coordinate information in latitude and longitude degrees, to the equivalent of six decimal places in degrees.

Line data have the advantage of allowing you and other viewers of your map to locate your point data within a framework of familiar landmarks such as streets or rivers. Data of this type typically are available from private or governmental sources in considerable detail. (In rapid-growth areas, the data need to be updated on a regular basis.) Every type of layer can be automatically turned on or off as a function of how closely the viewer has zoomed in on the map. This ability to selectively display detail is especially important with line data such as streets, which could otherwise make the map too busy to be of any practical use.

Polygon data describe a set of background layers that have a common characteristic, such as airports, county parks, census tracts, or bodies of water. These layers can help you develop meaningful insights by superimposing selected point data and pertinent polygon data. An example would be superimposing point locations for contaminated wells (point data) onto well field protection zones (polygon data). Suggest those polygon layers you think might be potentially useful on your map to your mapmaker.

[FIGURE 1 OMITTED]

A fourth, specialized, type of layer information is called ortho-photo data, available from both commercial and governmental sources. Ortho-photos project lifelike images of the landscape below with remarkable realism and level of detail (down to a typical resolution of six inches). These images take up massive amounts of electronic storage space, but when used selectively are very useful analytic tools. One or more point, line, or polygon layers of information can be selectively superimposed on an ortho-photo of a selected area. When imposed on an ortho-photo, the three conventional GIS layers can provide an enormous amount of useful map information.

Three practical types of maps are discussed below. Perhaps the simplest and most dramatic map is one that outlines an area of particular interest to the audience. It has dramatic impact and instantly conveys the message effectively. It does not require any spreadsheet, only a detailed knowledge of the area boundaries (roads, county line, etc.) and a certain level of manual dexterity in the use of the GIS drawing tool to outline the polygon. Since a map of this type is a "snapshot," its useful time period is limited. It is particularly useful for handouts and newspaper articles (Figure 1).

Another type of map also is effective in presenting summary information in a format that is easily understood by audiences. For example, the Palm Beach County Health Department wanted to emphasize that the distribution of new cases of AIDS was sharply different for zip codes within the county. The main advantages of such a map are impact in terms of readability and a clear communication of patterns that have been derived from relatively complex data. The disadvantages include a lack of comprehensive detail (Figure 2).

[FIGURE 2 OMITTED]

A third type of map that has proven useful to the Palm Beach County Health Department is an ortho-photo showing an area of interest with superimposed layers identifying roads and key census information. Such a map helped department staff analyze the neighborhood where an individual in one of the malaria cases of 2003 resided. It brought to staff attention a heavily wooded area to the south, where public health practitioners investigated homeless occupancy (Figure 3).

Engage in dialogue with your colleagues and assemble your own list of potential GIS projects. Be sure to include discussion of the payoffs. Only you and your colleagues can identify the GIS projects that may have significant and realistic payoff. A potential list might include the following GIS projects:

1. Potential bioterrorism-related applications--advance planning here can pay large dividends.

2. Natural-disaster assessment and remediation events--forest fires, hurricanes, and tornadoes are examples of such occasions.

3. Inventorying and mapping of sanitary infrastructure can be used for installations such as septic tanks, drinking-water wells, and lift stations.

4. Web-based dynamic maps, such as maps of child care centers may be of interest. The current ability to establish and maintain such maps is hampered by the lack of relatively inexpensive standardized software that is simple to use. As this situation changes, the demand for current dynamic maps will very substantially increase, and new Web-based maps will be installed in sharply increasing numbers.

Resource availability is a continuing problem for a "soft" application such as GIS. There is ample documentation of its benefits, as measured in savings of money and time, but these benefits are usually avoidance benefits. (GIS rarely produces "hard" savings of the type attractive to accountants and administrators, such as savings produced by reduction in personnel).

The major benefit of effectively utilizing GIS is the tremendous advantage of bringing fresh insight into the process of solving public health problems. These problem-solving insights are typically provided with little, if any, increase in personnel and only minor expenditures in one-time purchases of software and training. The application of these insights to public health situations can potentially avert major misapplication of scarce resources, and in some cases protect quality of life, life itself, or both. GIS is a potent tool. In the authors' view, the best way to justify its use is to point out that it is more and more becoming a weapon of choice in effectively combatting disease and threats to a healthy environment.

There also are some practical approaches to augmenting the scarce resources generally available to those developing and using GIS applications:

1. Network. Develop a network of cooperation within your organization and with colleagues in other organizations. Share your knowledge. Help each other solve problems. Collaborate on projects of potential benefit to your larger community. Share your scarce resources when feasible, including through temporary loans of specialized equipment. Palm Beach County, for instance, has a GIS Forum, which has been meeting bi-monthly for many years for just such networking purposes.

2. Maintain a proactive linkage with statewide and national databases. Work to achieve open standardized formats that can be easily shared. Fight parochialism. Let your vendors know you want open systems. Participate in areawide organizations, which provide training platforms both for members and for nonmembers. Anticipate changes in software, and proactively adapt and modify existing database structures to accommodate innovative improvements.

3. Employ GIS tools that are the wave of the future. Some of these tools are

* ortho-photo maps of high resolution;

* differentially corrected GPS systems tightly integrated with GIS software (these systems acquire latitude/longitude information, which readily permits mapping of geographic points); and

* standardized field inspection tools for acquiring and processing GIS location and attribute information, including powerful GIS-equipped handheld computers.

4. Expand GIS awareness throughout your organization. Be on the lookout for public health problem areas that might profit from the creative application of GIS.

Some caveats are in order. Don't be afraid to take on a project that has never been done before--it is the fastest way to acquire new knowledge. Be willing to make mistakes--just acknowledge them, correct them quickly, and make sure you share the lessons learned. Maintain open communication with everybody using GIS--everyone learns from each other. Finally, recognize that GIS may be very helpful in many situations, but that it is not the only approach to solving a particular public health problem.

[FIGURE 3 OMITTED]

In summary, take the time to plan your map before you expend any significant effort. Focus on the purpose of the map. You will be rewarded with a map that suits your purpose, is easily readable by your audience, and conveys your message with a strong visual impact. Carefully choose the information layers you want to include. Try to make the map location instantly recognizable to your audience. Utilize color to enhance the readability of individual locations, providing contrast where useful.

Then plan the map to provide knowledge without losing readability and impact. Judiciously use ortho-photos. Carefully label the map. Less information is better than too much.

Finally, multiply your resources by networking with your colleagues. Share your knowledge and scarce resources. Expand awareness of the benefits of GIS throughout your organization. Be fully open to challenge and innovation.

Suggested Additional Reading

Cromley, E., & McLafferty, S. (2002). GIS and Public Health. New York: Guilford Press. (ISBN: 1572307072.) This book offers a foundation for the understanding of geographic information systems (GIS). It explains basic concepts and demonstrates how to implement core data analysis techniques.

Korte, G. (2000). The GIS Book (5th ed.). Clifton Park, NY: OnWord Press. (ISBN: 0766828204.) This updated and expanded resource helps readers understand what a geographic information system is and what it can do.

Steede-Terry, K. (2000). Integrating GIS and the Global Positioning System. Redlands: ESRI Press. (ISBN: 1879102811.) The coupling of the global positioning system (GPS) with the geographic information system (GIS) is an information revolution that will give unprecedented accuracy in measurement and completeness of coverage. This comprehensive reference answers the myriad questions involved in combining these two systems for maximum benefit.

Robert H. Jenks, M.B.A.

Jean M. Malecki, M.D., M.P.H.

Corresponding Author: Robert H. Jenks, Environmental Specialist, Palm Beach County Health Department, Environmental Health & Engineering, 901 Evernia St., West Palm Beach, FL, 33402-0029, E-mail: [e-mail].